CN114674748A - A highly integrated photoacoustic gas sensor based on optical path optimization - Google Patents

Abstract

The invention discloses a highly integrated photoacoustic gas sensor based on optical path optimization, comprising a base plate, a casing forming a sealed air chamber with the base plate, and a radiation source arranged in the air chamber. The radiation source is arranged on the plug-in board; a light absorbing structure is arranged on the inner side wall of the housing away from the radiation source in the gas chamber, and several arc reflection structures are arranged on the inner side wall of the housing of the gas chamber. The arc reflection structure is distributed at the upper and lower positions of the inner side wall of the air chamber, and the light emitted by the radiation source reaches the light absorption structure after being reflected by several arc reflection structures; The air hole is covered with a waterproof and breathable film; a microphone, an ASIC chip and a control element are arranged on the substrate in the air chamber. The photoacoustic gas sensor disclosed in the invention achieves the purpose of miniaturization and integration, and can also improve detection accuracy, detection sensitivity and detection limit.

Description

A highly integrated photoacoustic gas sensor based on optical path optimization

technical field

The invention relates to the field of photoacoustic measurement, in particular to a highly integrated photoacoustic gas sensor based on optical path optimization.

Background technique

With the continuous development of society, the types of gases that people come into contact with in production and life are becoming more and more complex, and gas concentration detection has an increasingly important impact on production and life. Traditional gas detection methods include electrochemical methods, electrical methods, optical methods, etc. Among them, the gas sensor based on optical method has many advantages such as high sensitivity and good selectivity.

The photoacoustic effect refers to the phenomenon that gas absorbs modulated light and generates sound pressure. Its basic theory is the process of generating photoacoustic signals from light to heat to sound. A gas has a strong absorption peak for light of a certain wavelength, and different types of gases have strong absorption peaks for light of different wavelengths. After the gas absorbs the modulated light, a transition occurs, and the molecules that transition to the excited state release this part of the energy in some form, and the released energy is converted into heat energy. Gas concentration sensors based on photoacoustic effect often include four structures: radiation source, gas chamber, closed photoacoustic cell, and microphone. In a closed photoacoustic cell, the light signal generated by the gas absorption modulated light source will generate a heat signal of the same frequency. According to the ideal gas state equation, a pressure signal of the same frequency, that is, a photoacoustic signal, will be generated accordingly. The photoacoustic signal will increase with the increase of gas concentration, so the gas concentration can be detected according to the size of the photoacoustic signal.

The size of traditional photoacoustic gas sensors is often large, so that the light has a long enough optical path to be absorbed by gas molecules to ensure its detection accuracy, sensitivity, detection limit and other indicators. At the same time, closed photoacoustic cells are often bulky and require high packaging, making it difficult to miniaturize photoacoustic sensors. In addition, in the traditional photoacoustic gas sensor, the radiation source and the microphone usually need to be packaged independently and then repackaged into the sensor, which also leads to a low degree of integration, complicated use and high cost.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a highly integrated photoacoustic gas sensor based on optical path optimization, so as to realize a miniaturized and integrated photoacoustic gas sensor, and take into account indicators such as detection accuracy, detection sensitivity and detection limit.

For achieving the above object, technical scheme of the present invention is as follows:

A highly integrated photoacoustic gas sensor based on optical path optimization, comprising a substrate, a casing forming a sealed air chamber with the substrate, and a radiation source arranged in the air chamber, a plug board is vertically arranged on the substrate in the air chamber, and the The radiation source is arranged on the plug-in board; a light absorbing structure is arranged on the inner side wall of the housing away from the radiation source in the gas chamber, and a plurality of arc reflection structures are arranged on the inner side wall of the casing of the gas chamber. The reflective structures are distributed at the upper and lower positions of the inner side wall of the air chamber, and the light emitted by the radiation source is reflected by several arc reflection structures to reach the light absorbing structure; the air chamber is provided with air holes on the side, and the air holes are covered with waterproof A breathable membrane; a microphone, an ASIC chip and a control element are arranged on the substrate in the air chamber.

In one of the technical solutions, the radiation source is a MEMS light source, which is packaged in the form of QFN, and a condenser is provided outside the MEMS light source for condensing light to obtain near-collimated light to meet the needs of optical path design.

In another technical solution, the radiation source is a laser chip.

In a further technical solution, a light-transmitting heat-insulating casing is installed on the outside of the radiation source to prevent the photoacoustic signal from being disturbed by the heat signal generated by the self-heating of the radiation source.

In a further technical solution, a light-shielding casing is installed on the outside of the microphone, which can shield the interference of light to the microphone.

In the above solution, the microphone and the radiation source are packaged in the form of bare chips.

In the above solution, the substrate and the plug-in board are PCB boards.

In the above solution, the housing of the gas chamber is made of metal material or plastic material, and the inner wall is coated with film.

In a further technical solution, the waterproof and breathable membrane is a molecular sieve membrane with the function of screening molecules, which can play the role of isolating interfering gases such as water vapor, and can allow the gas to be detected to enter; it can also realize the selective entry of different types of gases.

In the above solution, the air hole and the light absorbing structure are located on the same inner side wall of the air chamber shell, which can reduce the influence on the light reflection.

Through the above technical solutions, a novel photoacoustic gas sensor based on optical path optimization provided by the present invention has the following beneficial effects:

1. There are several arc surface reflection structures on the inner side wall of the housing of the gas chamber of the present invention, and the arc reflection structures are distributed on the upper and lower positions of the inner side wall of the housing of the gas chamber, and the light emitted by the radiation source arranged on the plug board is After several arc reflection structures, the light can have a long enough optical path to be absorbed by the gas molecules, which is conducive to the detection of the gas to be tested with a very low concentration.

2. The present invention omits the traditional airtight photoacoustic cell, combines the air chamber with the airtight photoacoustic cell, greatly reduces the size, and avoids the complex packaging of the airtight photoacoustic cell.

3. The present invention encapsulates the radiation source and the microphone in the form of bare chips, and finally encapsulates them as a whole with the air chamber. Compared with the traditional form in which each component is individually packaged to form a complex system, the packaging method proposed by the present invention greatly improves the sensor performance. The degree of integration and miniaturization reduces process requirements.

4. In the present invention, a curved surface reflection structure is arranged on the inner side wall of the housing of the air chamber, and the radiation source is arranged on a plug-in board perpendicular to the base plate, so that the light is reflected between the inner side walls of the housing, compared with In the case of arranging the radiation source on the base plate and allowing the light to be reflected between the base plate and the top plate, the present invention only needs to process the inner side wall of the casing, which saves a separate processing procedure for the base plate, and greatly saves cost and processing. the complexity.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are required in the description of the embodiments or the prior art.

1 is a side view of a highly integrated photoacoustic gas sensor based on optical path optimization disclosed in Embodiment 1 of the present invention;

2 is a top view of a highly integrated photoacoustic gas sensor based on optical path optimization disclosed in Embodiment 1 of the present invention;

3 is a side view of a highly integrated photoacoustic gas sensor based on optical path optimization disclosed in Embodiment 2 of the present invention;

4 is a top view of a highly integrated photoacoustic gas sensor based on optical path optimization disclosed in Embodiment 2 of the present invention.

In the figure, 1, substrate; 2, plug-in board; 3, air chamber; 4, air hole; 5, waterproof and breathable membrane; 6, MEMS light source; 7, condenser lens; 8, thermal insulation shell; 9, microphone; 10, ASIC chip ; 11, control element; 12, arc reflection structure; 13, collimated light; 14, light absorption structure; 15, laser chip; 16, shell;

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

Example 1

The present invention provides a highly integrated photoacoustic gas sensor based on optical path optimization, as shown in FIG. In this embodiment, the casing 16 has a rectangular parallelepiped structure, and may also be a cube, a hemisphere, or the like. The substrate 1 plays the role of carrying internal components and providing circuit connections between the internal components. The air hole 4 is opened on the side shell 16 of the air chamber 3, which is used to communicate with the external gas environment, so that the air chamber 3 is filled with the gas to be measured; They are connected in an airtight manner such as bonding, so that an acoustically sealed structure is formed in the air chamber 3 . The waterproof and breathable membrane 5 can be selected from materials such as polymers.

A microphone 9 , an ASIC chip 10 and a control element 11 are arranged on the substrate 1 in the air chamber 3 . The ASIC chip 10 is used to control, pre-amplify, etc. the signal of the microphone 9 , and the control element 11 is used to control the radiation source and the microphone 9 . The selection of the microphone 9 is not limited to the common silicon-based microphones. The silicon-based condenser microphones and other forms of pressure sensors can be used to detect sound pressure signals and convert them into electrical signals. The technical solution provided by the present invention is applicable to any sound transmission element. In addition, the microphone 9 can be packaged in the form of a bare chip, which can simplify the system and improve the integration. The outside of the microphone is installed with a light-shielding casing that does not affect the coupled sound, which can shield the interference of light to the microphone.

A plug board 2 is vertically arranged on the substrate 1 in the air chamber 3, the plug board 2 is arranged at a position close to one side of the air chamber 3, and the radiation source is arranged on the plug board 2. In this embodiment, the radiation source is MEMS The light source 6 is packaged in the form of QFN. Due to the large divergence angle of the MEMS light source 6, a condenser lens 7 is fabricated on the QFN package shell outside the MEMS light source 6 for condensing light to obtain near-collimated emitted light to meet the optical path design. needs. A light-transmitting adiabatic casing 8 is installed on the outside of the radiation source to prevent the photoacoustic signal from being interfered by the heat signal generated by the heat generated by the radiation source itself.

As shown in FIG. 2 , a plurality of arc reflection structures 12 are arranged on the inner side walls of the two opposite shells 16 of the gas chamber 3 , and the arc reflection structures 12 are distributed on the upper and lower positions of the inner side walls of the shell 16 of the gas chamber 3 . The light emitted by the radiation source disposed on the plug board 2 passes through several arc reflection structures 12 between the inner side walls of the two shells 16 in the entire air chamber 3, and is reflected multiple times according to the designed optical path, which can make The light has a long enough optical path to be absorbed by the gas molecules, which is conducive to the detection of the gas to be tested with a very low concentration. The shell 16 of the gas chamber 3 of the present invention can be made of metal material, and the gas chamber 3 with the curved surface reflection structure 12 on the inner side wall can be obtained by machining, and then polished to obtain a smooth reflection surface, which is not very good for the reflectivity. The high metal material can be coated on its surface (gold, copper, aluminum, etc.) to further increase the reflectivity; or the housing 16 can also be made of plastic material, and the air chamber 3 with the curved surface reflection structure 12 on the inner side wall is integrally formed by injection molding process. , the formed inner side wall can also get a smooth reflective surface, at this time, the inner wall needs to be coated (gold, copper, aluminum, etc.) to improve the reflectivity.

A light-absorbing structure 14 is arranged on the inner side wall of the housing 16 in the air chamber 3 away from the radiation source. The light-absorbing structure 14 can be a light-absorbing coating, such as black glue and other materials with black and rough surface characteristics; the light emitted by the radiation source passes through several arcs. The surface reflection structure 12 reaches the light absorbing structure 14 after being reflected, and is finally absorbed by the light absorbing structure 14. The purpose of designing the light absorbing structure 14 is to prevent the light from being reflected multiple times in the gas chamber 3 and cannot be absorbed in time, which affects the next light output. detection.

In this embodiment, the substrate 1 and the plug board 2 are PCB boards, such as FR4, organic polymers, aluminum substrates, and the like.

In this embodiment, the microphone 9 and the radiation source are packaged in the form of bare chips, omitting the independent packaging of each device, and placing each device in the gas chamber 3 for overall packaging, which greatly improves the degree of integration and miniaturization.

In this embodiment, the air hole 4 and the light absorbing structure 14 are located on the same inner side wall of the housing 16 of the air chamber 3, which can reduce the influence on light reflection.

In particular, the waterproof and breathable membrane can use a molecular sieve membrane with the function of screening molecules, such as a molecular sieve membrane made of zeolite. function, and can communicate with the external gas environment, so that the gas to be detected can enter. In addition, through the control of the pore size of the molecular sieve, the selective entry of different types of gases can also be realized.

Example 2

Compared with Embodiment 1, the difference of this embodiment is that the laser chip 15 is selected as the radiation source, such as a vertical cavity surface emitting laser (vcsel) that can be integrated, as shown in FIG. 3 and FIG. 4 , because the laser chip 15 itself Collimated light 13 can be obtained without the need for a condenser 7 design.

In addition, there are various choices for radiation sources and various forms of optical path design, which are not limited to the shape of the housing 16 exemplified in the present invention. As long as the radiation source capable of emitting the collimated light 13 is packaged in the three-dimensional form proposed by the present invention, and the multiple reflection structures between the side walls are designed to optimize the optical path, it belongs to the protection scope of the present invention.

The detection principle of the photoacoustic gas sensor of the present invention is as follows:

When there is no detection gas in the gas chamber 3, the light signal generated by the radiation source will not be absorbed in the gas chamber 3, so no corresponding heat signal will be generated, and no sound pressure signal will be generated. When the detection gas exists in the gas chamber 3 , the detection gas will absorb part of the light, therefore, a corresponding sound pressure signal will be generated in the gas chamber 3 , which is detected and output by the microphone 9 . According to the photoacoustic theory, in this embodiment, as the detected gas concentration in the external environment increases, the photoacoustic signal increases; according to the magnitude of the output photoacoustic signal, the detected gas concentration can be reversed.

The beneficial effect of multiple reflections by optimizing the optical path is that the integrated photoacoustic sensor cannot detect the lower target gas concentration because the size of the housing 16 is often small and the optical path is not optimized. The optical path optimization structure designed by the present invention enables the detection gas and the light to be fully contacted and absorbed due to the multiple reflections of the light, so the final generated acoustic signal will be more obvious.

Obviously, the photoacoustic gas sensor without optimized design of the optical path is limited by the detection accuracy, detection limit and detection sensitivity, which makes it difficult to miniaturize and integrate; such indicators are not ideal. Thanks to the design of the air chamber 3 and the three-dimensional packaging of the radiation source, in the present invention, the light is reflected multiple times between the side walls of the air chamber 3 to optimize the optical path. input to large-scale traditional photoacoustic sensors. While realizing miniaturization and integration, the detection limit, detection sensitivity, detection accuracy and other indicators are taken into account. At the same time, compared to placing the radiation source on the substrate 1, the reflection structure between the substrate 1 and the gas chamber 3 is obtained by electroplating on the substrate 1. The present invention omits the processing procedure of the substrate 1, which greatly saves cost and processing. the complexity. At the same time, the air chamber 3 is manufactured by, for example, an injection molding process, taking into account the cost reduction. Under the same performance index, the size is about 20% to 40% of the traditional photoacoustic sensor.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A high-integration photoacoustic gas sensor based on optical path optimization is characterized by comprising a substrate, a shell forming a sealed gas chamber with the substrate and a radiation source arranged in the gas chamber, wherein a plugboard is vertically arranged on the substrate in the gas chamber, and the radiation source is arranged on the plugboard; a light absorption structure is arranged on the inner side wall of the shell, far away from the radiation source, in the air chamber, a plurality of cambered surface reflection structures are arranged on the inner side wall of the shell of the air chamber, the cambered surface reflection structures are distributed at the upper and lower positions of the inner side wall of the shell of the air chamber, and light emitted by the radiation source reaches the light absorption structure after being reflected by the cambered surface reflection structures; the side surface of the air chamber is provided with an air hole, and a waterproof and breathable film covers the air hole; a microphone, an ASIC chip and a control element are arranged on the substrate in the air chamber.

2. The optical path optimization-based highly integrated photoacoustic gas sensor of claim 1, wherein the radiation source is a MEMS light source, which is packaged in QFN format, and a condenser lens is disposed outside the MEMS light source.

3. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the radiation source is a laser chip.

4. A highly integrated photoacoustic gas sensor based on optical path optimization according to claim 2 or 3, wherein the radiation source is externally mounted with a light-transmissive heat-insulating enclosure.

5. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the light-shielding housing is installed outside the microphone.

6. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the microphone and the radiation source are packaged in a bare chip form.

7. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the substrate and the patch board are PCB boards.

8. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the housing of the gas chamber is made of metal or plastic and the inner wall of the gas chamber is coated with a film.

9. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the waterproof gas permeable membrane is a molecular sieve membrane with a molecular sieving function.

10. The highly integrated photoacoustic gas sensor based on optical path optimization of claim 1, wherein the air holes and the light absorbing structures are located on the same inner sidewall of the gas cell housing.

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